Catheters having exterior coatings have been known for many years. Typically the coating is a hydrophilic layer designed to reduce the coefficient of friction in the wet condition, so that the catheter may be inserted relatively painlessly into the urethra of the patient, and likewise removed therefrom when required.
Typical examples of such catheters are made known in European patent specifications EP-B-0093093 (Astra Meditec AB) and EP-B-0217771 (Astra Meditec AB). EP-B-0093093 discloses a process for providing a polymer surface, such as a urinary latex catheter, with a primary coating including an isocyanate compound, and a secondary coating including polyvinylpyrrolidone. EP-B-0217771 discloses a method of forming an improved hydrophilic coating in order to retain the slipperiness for a longer time on a substrate, such as a urinary PVC catheter, by applying a solution comprising a solvent having an osmolality-increasing compound such as sodium chloride.
Catheters are conventionally packaged in a paper package, in order to allow them to be sterilized before they are used. Such sterilization typically is performed at the time of manufacture, using techniques well-known in the art such as gamma-irradiation or fumigation with ethylene oxide gas. If ethylene oxide is used, it must be allowed to have access to the catheter surface, and a paper package allows this to occur. The conventional approach is to use a paper which is permeable to ethylene oxide, grid-lacquered with polyethylene and welded around its edge to a laminate of, for example, polyethylene-polypropylene or polyethylene-polyethylene terephthalate, or possibly polyethylene-nylon.
Applicant has observed that a problem encountered with coated catheters is that the surface of the catheter can become sticky and adhere to the paper of the package causing the coating on the catheter to be damaged, destroyed or mutilated.
Inserting a plastics material adjacent to the interior surface of the paper has been suggested, creating a loose paper-plastic laminate sealed just around its edges so that the catheter does not come into immediate contact with the paper. However, this has the disadvantage that a barrier is now in place which prevents penetration of ethylene oxide into the interior of the package so as to be brought into contact with the surface of the catheter. Such a package could only effectively be sterilized by irradiation, although an alternative is to provide a number of slits in the plastics material, thin enough to prevent the catheter surface from coming into direct contact with the paper and yet capable of opening wide enough to allow access of ethylene oxide at the required time.
This clearly means that the manufacturing process is made more complicated than would be desirable. In particular, the slits in the plastics material have to be carefully regulated so that they do not permit contact of the catheter surface with the paper, without in any way hindering sterilization with ethylene oxide.